Make edebug see unused variables when lexical-binding is non-nil

This fixes bug #59213.

* lisp/emacs-lisp/cconv.el (cconv-dont-trim-unused-variables): New variable.
(cconv-fv, cconv-make-interpreted-closure): Add/amend doc strings.
(cconv-make-interpreted-closure): Test cconv-dont-trim-unused-variables, and
if non-nil, don't "optimize" the lexical environment.

* lisp/emacs-lisp/edebug.el (edebug-make-enter-wrapper): Compile a binding of
cconv-dont-trim-unused-variables to t around the call of edebug-enter.

* lisp/emacs-lisp/testconver.el (testcover-analyze-coverage): Add a new arm to
the pcase form to handle the new form of edebug-enter.

3 files changed, 38 insertions, 18 deletions

diff --git a/lisp/emacs-lisp/cconv.el b/lisp/emacs-lisp/cconv.el
index 570c9e66060..b8121aeba55 100644
--- a/lisp/emacs-lisp/cconv.el
+++ b/lisp/emacs-lisp/cconv.el
@@ -113,6 +113,10 @@ is less than this number.")
 (defvar cconv--dynbound-variables nil
   "List of variables known to be dynamically bound.")
 
+(defvar cconv-dont-trim-unused-variables nil
+  "When bound to non-nil, don't remove unused variables from the environment.
+This is intended for use by edebug and similar.")
+
 ;;;###autoload
 (defun cconv-closure-convert (form &optional dynbound-vars)
   "Main entry point for closure conversion.
@@ -834,10 +838,13 @@ This function does not return anything but instead fills the
 (define-obsolete-function-alias 'cconv-analyse-form #'cconv-analyze-form "25.1")
 
 (defun cconv-fv (form lexvars dynvars)
-  "Return the list of free variables in FORM.
-LEXVARS is the list of statically scoped vars in the context
-and DYNVARS is the list of dynamically scoped vars in the context.
-Returns a pair (LEXV . DYNV) of those vars actually used by FORM."
+  "Return the free variables used in FORM.
+FORM is usually a function #\\='(lambda ...), but may be any valid
+form.  LEXVARS is a list of symbols, each of which is lexically
+bound in FORM's context.  DYNVARS is a list of symbols, each of
+which is dynamically bound in FORM's context.
+Returns a cons (LEXV . DYNV), the car and cdr being lists of the
+lexically and dynamically bound symbols actually used by FORM."
   (let* ((fun
           ;; Wrap FORM into a function because the analysis code we
           ;; have only computes freevars for functions.
@@ -875,11 +882,19 @@ Returns a pair (LEXV . DYNV) of those vars actually used by FORM."
         (cons fvs dyns)))))
 
 (defun cconv-make-interpreted-closure (fun env)
+  "Make a closure for the interpreter.
+This function is evaluated both at compile time and run time.
+FUN, the closure's function, must be a lambda form.
+ENV, the closure's environment, is a mixture of lexical bindings of the form
+(SYMBOL . VALUE) and symbols which indicate dynamic bindings of those
+symbols."
   (cl-assert (eq (car-safe fun) 'lambda))
   (let ((lexvars (delq nil (mapcar #'car-safe env))))
-    (if (null lexvars)
-        ;; The lexical environment is empty, so there's no need to
-        ;; look for free variables.
+    (if (or cconv-dont-trim-unused-variables (null lexvars))
+        ;; The lexical environment is empty, or needs to be preserved,
+        ;; so there's no need to look for free variables.
+        ;; Attempting to replace ,(cdr fun) by a macroexpanded version
+        ;; causes bootstrap to fail.
         `(closure ,env . ,(cdr fun))
       ;; We could try and cache the result of the macroexpansion and
       ;; `cconv-fv' analysis.  Not sure it's worth the trouble.
@@ -896,7 +911,7 @@ Returns a pair (LEXV . DYNV) of those vars actually used by FORM."
               (pcase expanded-form
                 (`#'(lambda . ,cdr) cdr)
                 (_ (cdr fun))))
-         
+
              (dynvars (delq nil (mapcar (lambda (b) (if (symbolp b) b)) env)))
              (fvs (cconv-fv expanded-form lexvars dynvars))
              (newenv (nconc (mapcar (lambda (fv) (assq fv env)) (car fvs))
diff --git a/lisp/emacs-lisp/edebug.el b/lisp/emacs-lisp/edebug.el
index 2f7d03e9d79..735a358cdba 100644
--- a/lisp/emacs-lisp/edebug.el
+++ b/lisp/emacs-lisp/edebug.el
@@ -1217,16 +1217,16 @@ purpose by adding an entry to this alist, and setting
     (setq edebug-old-def-name nil))
   (setq edebug-def-name
         (or edebug-def-name edebug-old-def-name (gensym "edebug-anon")))
-  `(edebug-enter
-    (quote ,edebug-def-name)
-    ,(if edebug-inside-func
-         `(list
-           ;; Doesn't work with more than one def-body!!
-           ;; But the list will just be reversed.
-           ,@(nreverse edebug-def-args))
-       'nil)
-    (function (lambda () ,@forms))
-    ))
+  `(let ((cconv-dont-trim-unused-variables t))
+     (edebug-enter
+      (quote ,edebug-def-name)
+      ,(if edebug-inside-func
+           `(list
+             ;; Doesn't work with more than one def-body!!
+             ;; But the list will just be reversed.
+             ,@(nreverse edebug-def-args))
+         'nil)
+      (function (lambda () ,@forms)))))
 
 
 (defvar edebug-form-begin-marker) ; the mark for def being instrumented
diff --git a/lisp/emacs-lisp/testcover.el b/lisp/emacs-lisp/testcover.el
index ed31b90ca32..1212905f08a 100644
--- a/lisp/emacs-lisp/testcover.el
+++ b/lisp/emacs-lisp/testcover.el
@@ -442,6 +442,11 @@ or return multiple values."
      (let ((testcover-vector (get sym 'edebug-coverage)))
        (testcover-analyze-coverage-progn body)))
 
+    (`(let ((cconv-dont-trim-unused-variables t))
+        (edebug-enter ',sym ,_ (function (lambda nil . ,body))))
+     (let ((testcover-vector (get sym 'edebug-coverage)))
+       (testcover-analyze-coverage-progn body)))
+
     (`(edebug-after ,(and before-form
                           (or `(edebug-before ,before-id) before-id))
                     ,after-id ,wrapped-form)